Many models for the control of gene expression in higher cells have been proposed in recent years. These models suggest a variety of mechanisms for exerting this control both at the level of the initiation of RNA transcription and at subsequent RNA modification and processing steps. Crucial to the evaluation and testing of these models is a description at the molecular level of the pathway being controlled. The overall objective of the proposed studies is to elucidate the pathway which leads to the production of a cytoplasmic messenger RNA. This will involve: (1) the isolation and characterization of cloned DNA segments of Drosophila DNA which contain the structural gene for an abundant mRNA; (2) structural analysis of the mRNA and; (3) determination of the structure and metabolism of the primary gene transcription product in various cell types and stages of development.